Workup was negative for neuromyelitis optica [NMO] (negative CSF anti-NMO IgG, negative serum NMO/AQP-4 IgG), varicella zoster virus (VZV), enterovirus, herpes simplex viruses (HSV) 1 and 2, human T-cell lymphotropic viruses I and II, HIV, syphilis, B12 or folate deficiency, sarcoidosis, vertebral dissection, multiple sclerosis (negative CSF IgG index and oligoclonal bands), acute disseminating encephalomyelitis (normal brain MRI), spinal arteriovenous malformation/cavernoma and dural arteriovenous fistula, inherited hypercoagulopathies, cryoglobulinemia, and systemic autoimmune diseases. Here, AQP4 is linked to neuromyelitis optica.